BTU Calculator
BTU/hr cooling capacity for an air conditioner sized to a room.
Formula
BTU = Area × 25 × sun × ceiling + kitchen + people
How to use
- 1Enter the room length, width and ceiling height.
- 2Choose the sun exposure and whether it is a kitchen.
- 3Enter how many people are usually in the room.
- 4Read the required BTU/hr and recommended tonnage.
About this calculator
An air conditioner that is too small runs constantly without cooling; one too large cools so fast it switches off before removing humidity, leaving the room cold and clammy. Getting the size right comes down to BTUs of cooling capacity. This calculator estimates how many your room needs from its size, sun exposure, use and occupancy.
Formula explained
BTU = Area × 25 × sun factor × ceiling factor + kitchen + extra people. Area is length × width (ft), 25 is the base BTU per square foot, and the sun and ceiling factors adjust for brightness and room height. A kitchen adds about 4000 BTU; each person beyond two adds about 600. Divide the total by 12,000 for tons of cooling.
Worked example
Area 168 ft² × 25 = 4200 BTU. Average sun and a standard ceiling keep both factors at 1, and two people add nothing, so about 4200 BTU/hr - a small unit.
Tips & notes
- Measure the room carefully, including ceiling height, and be honest about sun and occupancy.
- Lean slightly higher in a hot, humid climate or a poorly insulated room.
- Between two sizes, weigh insulation and sun rather than automatically rounding up.